PHYS 162 1

Life in the Universe

• 1 example of Life - Carbon-water based

• 1 example of “intelligence” which has been able to

communicate with other “intelligent” life for about 70 years

• intelligence= able to use Radio to send/receive messages

• chemical building blocks (amino acids, water) plentiful in

interstellar space

• Somehow about 1 billion years after the Earth formed,

bacteria appeared. All other life are probably descendants

PHYS 162 2

Life – Carbon+Water based?

“Ammonia! Ammonia!”

@R. Grossman 1962 New Yorker

Carbon vs Silicon? NO

Water vs other liquid or

gas? Not sure but water

seems to be the best

medium in which

biochemistry takes place

PHYS 162 3

Life on Earth

• about 4.5 billion years ago Earth

formed. About 1.5 billion years

after that simple bacteria

(prokaryote) appeared

• About 2 billion years after,

complex life (eukaryote)

appeared including algae which

though photosynthesis started

releasing oxygen

• atmosphere changed, probably

keeping warm enough so end of

“iceball Earth”??

Takes billions of years for

complex life to develop

PHYS 162 4

Life on Earth

• appears as if all current life descended from same

ancestor

• all use DNA and RNA and amino acids

• all use ATP for storing/using energy

• amino acids come in both left-handed and right-

handed versions. All life uses left-handed

exclusively

PHYS 162 5

Other Life in Solar System?

• there is, or has been, liquid water on Mars and

various moons of Jupiter (Europa, Ganymede,

Callisto) and Saturn (Titan, Enceladus) look for

signs of life.

• If ever find, is it of different origin then Earth’s? Say

right-handed amino acids show independent origin

• more info about Mars then anywhere else: both

meteors from Mars and the many landings on the

surface

PHYS 162 6

Best Bet: Moons of Jupiter and Saturn

PHYS 162 7

Life on Mars? • landings on the surface have not shown any evidence

• BUT 16 million years ago, an asteroid slammed into

Mars, Mars rock thrown into space, drifted, and landed in

Antarctica 13,000 years ago, results in 1996

• tell from Mars by chemical and gas composition

• possible indications (tubelike objects, hydrocarbons) of

bacteria fossils from 3.6 billion years ago

• no agreement among experts (in Chapter 5)

PHYS 162 8

Extra Terrestrial Intelligence

• is there intelligent life on other planets?

Drake equation estimates possibility in our

galaxy

• can we try to communicate?

SETI = Search for Extra Terrestrial

Intelligence

PHYS 162 9

Drake Equation

• N = number of “intelligent” civilizations in the Galaxy

• R* = rate at which solar type stars are formed

• fp = fraction of stars which have planets

• ne = number of planets suitable for life

• fl = fraction of planets where life arises

• fi = fraction of life that develops intelligence

• fc = fraction of intelligent life that communicates

• L = lifetime of communicating intelligence

LfffnfRN cilep

PHYS 162 10

Possible Stars

Stars can’t be

• too large. Need lifetime more than 2 billion years

• too small. Need habitable region not too close to

star

• too old. Need heavy elements C,O,N in “young”

stars

• in binary system. Planet’s orbit complicated.

Temperature varies

PHYS 162 11

Possible Planets

Planets can’t be

• too large or too small want atmosphere, and

probably want water

• too hot or too cold want temperature so water is

a liquid

• habitable zone about a star. For larger/hotter

stars this will be further away

PHYS 162 12

Habitable Zone

PHYS 162 13

Habitable Zone

PHYS 162 14

Evolution of Intelligence

• How probable is the evolution from simple to complicated to

intelligent life?

• How probable is the development of technology?

NOT VERY

• dolphins do not need technology (and neither do some human

cultures)

• How did humans evolve?

opposable thumb

communication

slow and weak

tools technology in some cultures but not in others

PHYS 162 15

Length of Survival of “Intelligence”

• for human culture, anyone’s guess. 100 to

100,000,000 years

• large asteroid

• environmental catastrophes (global warming,

ozone, insecticides)

• nuclear/biological war

• plague

Most species are extinct

• humans could also become uninterested in SETI

PHYS 162 16

Asteroids, Comets and Meteors

PHYS 162 17

Asteroids, Comets and Meteors

Meteor crater in

Yucatan, from

65,000,000 years ago

Meteor crater in

Arizona, from 50,000

years ago

PHYS 162 18

Near Earth Asteroid Tracking NEAT

Look for and track all objects > 1 km in

diameter, close to Earth. ~1200 are “potentially

hazardous”

PHYS 162 19

Near Earth Asteroids

(29075) 1950 DA is notable for having the highest known

probability of impacting Earth (between 0 and 0.33%). Would

happen on March 16, 2880. But orbit can change with time....

mass about 3

billion tons

PHYS 162 20

Drake Equation – guess at values

• R* = rate at which solar type stars are formed 1 per year

• fp = fraction of stars which have planets 1

• ne = number of planets suitable for life 0.01 - 0.1 ??

• fl = fraction of planets where life arises 0.001 - 0.1 ?????

• fi = fraction of life that develops intelligence 0.0001 - 0.5 ???????

• fc = fraction of intelligent life that communicates 0.0001- 0.9 ??????

• L = lifetime of communicating intelligence 100 - 25,000 years ????

• N = # of “intelligent” civilizations in the Galaxy = 100 (optimistic)

• N = number of “intelligent” civilizations in the Galaxy = 1 (us

possibly realistic)

PHYS 162 21

Communicating with ET

• send a spaceship

too slow. velocity is at most .001 times light speed so

more than 1000 years to nearest star

• send a radio/TV message (and listen for them)

travels at speed of light over a wide area

What frequency?

What message?

What direction? maybe in time have a list of found

Earth-like exoplanets

PHYS 162 22

Communicating with ET spacecraft

• covers why

space travel

will always be

“slow”

PHYS 162 23

Communicating with ET: spacecraft

• Pioneer 10+11 and

Voyager I+II launched

in 1973+1977

• Now beyond Pluto. Can

still communicate with

the Voyager crafts who

are at 117 AU from Sun

• contain plaques and

records for ET to find

PHYS 162 24

• Pioneer plaque

• Voyager record includes “Hello”

in many languages, Richard

Nixon, and 90 minutes of music

from Javanese to Bach to Chuck

Berry

• SNL joke. first message from

aliens “send more Chuck Berry”

PHYS 162 25

Communicating with ET: Radio

What frequency? Microwave is most quiet.

Maybe near one of water’s frequencies?

21 cm is the

Hydrogen

spin-flip

wavelength

PHYS 162 26

Communicating with ET: Radio

What message? See movie Contact (from Carl

Sagan’s book). Signal sent in 1974

23 columns by 73 rows = 1679 bits (either 0 or 1)

PHYS 162 27

numbers 1 to 10

elements H (1) C(6) N(7) O(8) P(15)

nucleotides (like phosphate and adenine)

DNA double helix including the number of

base pairs in human genome

human with height (left) and population (right)

9 planets plus Sun with Earth shifted

Arecibo telescope with diameter noted on

bottom